COI gene tree calculated with FastTree2 ver. 2.1.5 (Price et al. 2010) with the GTR plus gamma model and 20 rate categories of sites to estimate initial gene trees from the sequences. Support values were calculated for nodes with the Shimodaira-Hasegawa (Shimodaira and Hasegawa 1999) test and 1000 resamples. Samples via IceAGE, NorAmph and mined from Genbank (Details Supplementary Table 1). Clades are coloured for depth strata for sampling: 0–200 m light grey, 201–500 m light green, 501–1000 m turquoise, 1000+ m blue. A combination of vertical colours indicates a combination of depth strata.